The present invention relates to a driving head which can be used for pneumatic ramming apparatus or pile drivers and can also serve as an attachment head for rods or pipes which are to be driven or forced in by means of ramming apparatus or pile drivers. The driving head has an essentially circular front end, and a conically expanding surface over the periphery of which are uniformily distributed a plurality of longitudinal grooves which start from the front end. Also provided is at least one transversely extending section which extends around the surface of the driving head in a circular manner.
If articles are to be driven into the earth vertically, horizontally, or at an angle, the shape of the end of the article has a determinative effect upon the size and type of the resistance to penetration, which resistance is composed of an end resistance which acts on the front, and the surface friction which occurs on the lateral peripheral surfaces.
When a narrow conical head is driven into the ground, essentially only radial forces occur which are transmitted in proportion to the cone inclination. If, for example, the cone has an inclination of 1:10, the sum of the radial forces is ten times as great as the sum of the driven axial forces. A narrow cone therefore enters the earth very easily. However, since in order to obtain a state of equilibrium, the sum of all of the radial forces must be the same, a narrow cone is easily deflected sideways out of its intended direction when it encounters slight resistance.
However, the accuracy with which articles travel when entering the ground is often very significant, such as when driving in the rods or power drills, or steel pipes for obtaining ground water, and also when forcing pipes through or when using earth displacement hammers. To improve the accuracy of travel, the conical end of heretofore known devices was therefore replaced by a stepped head according to which the covering of the steps formed a conical shape which is embodied as a stepped surface yet is cylindrical. With such a driving head, the end faces of the steps conduct axial pushing and impact components into the ground. Under the effect of this axially directed force, with a slight radial tendency, the ground ahead of the end of the entering driving head is rearranged and homogenized. In so doing, loose areas receive more earth particles than do more densely packed areas, so that the radial resistance about the axis of the driving head is nearly uniform due to the rearrangement and homogenizing. The end faces of the steps can also apply fragmenting and rotary pulses in boulders, stones, or gravel, and can therefore positively affect the displacement process, especially when the driving head is not only pushed in statically, but is also dynamically driven in.
Despite the aforementioned advantages of a stepped head shape, the heretofore known devices have the drawback that a greater consumption of energy is required in order to press or drive the head into the ground. Furthermore, there exists the danger that the axial pushing and impact components will compress the ground ahead of the driving head in such a way that the entry of the head is brought to a halt. A particular problem occurs with fine sandy soil, the granular size of which is nearly uniform, i.e. with so called-single-grain soil which cannot be easily compacted and hence can also not be easily displaced.
It is an object of the present invention to provide a shape for a driving head of the aforementioned general type which, while providing as accurate a travel as possible, provides a reduction of the resistance to entry.